Different Effects of Long-Term Grazing Exclusion and Growth Stages on Soil Fungi and Bacteria in an Alpine Steppe on the Qinghai-Tibetan Plateau

Changes in soil microorganisms caused by enclosure have long been an important topic in grassland ecology. However, few studies have described the responses of the soil microbial community composition, functional groups, and co-occurrence networks at different growth stages to long-term grazing exclusion or compared the indicative abilities of diversity and network parameters on soil ecosystem functions after grazing exclusion. In this study, we conducted a field experiment to evaluate the response of soil microbes to long-term grazing exclusion in an alpine steppe on the Qinghai-Tibetan Plateau. Our results showed that both soil fungal and bacterial community compositions at different growth stages showed significant differences. However, the enclosure only altered the fungal community composition. Differences in soil microbial functional groups between fungi and bacteria were also detected. The leading group in soil fungi was governed by grazing exclusion, and most bacterial functional groups showed significant differences between the growth stages. The co-occurrence network patterns of the fungi and bacteria differed significantly. Unexpectedly, the enclosure did not significantly alter the fungal or bacterial co-occurrence networks. Network parameters had a stronger ability to indicate soil ecosystem functions than the diversity index, displaying better relationships between network parameters and soil organic carbon and nitrate. These findings suggest that elucidating the responses of soil microbes at different growth stages is necessary to comprehensively understand soil ecosystems after long-term grazing exclusion in the alpine steppe.